1. Field of Invention
The inventive subject matter relates to an acoustic-electronic stethoscope capable of selectively amplifying sounds of medical importance while suppressing environmental background noises. The inventive stethoscope contains an innovative chest piece design and employs simplistic circuitry to emulate the sound quality of standard acoustic stethoscopes. The inventive stethoscope is rugged, water resistant, and simple to operate.
2. Description of the Related Art
Physicians and other health care workers use stethoscopes in order to evaluate sounds emanating from tissue sources, primarily heart and lung. Evaluation of these internal organs is via the transmission of the sound energy through the skin. Classic stethoscope design attempts to minimize the area of skin evaluated for sound transmission as well as minimizing the effects of outside environmental noise. However, with environments with increasing ambient noise, such as in busy hospitals and outside field settings, ambient environmental noise is becoming an increasing issue in the ability to properly discriminate and evaluate relevant sounds from background noise. Additionally, traditional acoustic stethoscopes introduce many distortions in its signal. Many of these distortions are the result of standing waves in the long tubes.
Non-traditional sensors that are adhered to the skin avoid some of the environmental noise distortions but they have relatively small output signals, which must be amplified. Thin-film piezoelectric materials adhered to skin can sense skin vibration caused by body sounds. Vibration of the skin causes minute flexion of the sensor that generates an electrical signal. However, adherent sensors present the user with several inconveniences including: patients with body hair must be shaved at all locations of interest; because of the adhesive, moving the sensor from location to location is slow and therefore not practical for even routine examinations; the user must take extreme care to avoid extraneous noise caused by anything that touches the sensor or its lead wire.
Noise sources that are problematic for all electronic stethoscopes include: environmental noise that couples into the sensor within the chest piece and is therefore mixed with sounds of interest before entering the electronic circuitry; noise that couples into the unit and gets conveyed to the user's ears through the head set tubes; environmental noise and mechanical vibrations that enter the patient through epidermal tissue and subsequently detected by the sensor; environmental noise that enters the user's ears directly; muscle tremor noise that is caused by holding the chest piece and detected by the sensor; electromagnetic pick-up (interference). While none of these can be totally eliminated, the present invention has design features that reduce most of them.
Attempts have been made to develop noise-tolerant stethoscope-like systems based on active noise-cancellation technology. These devices tend to be large and impractical for field use. And they have had limited success in reducing noise because upon entering the human body, noise characteristics are dramatically transformed in ways that differ substantially from person to person. It is therefore impossible to sample the environmental noise with a separate sensor and then subtract that noise from sounds of interest. Further their inherent complexity of design, such as the inclusion of an additional pick-up and electronics, adds cost and complexity, thus making these devices unsuitable for field use such as in the military or ambulance. Therefore, a need exists for sensitive, sound discriminating stethoscopes that are both rugged and simple and therefore less prone to mechanical failure, especially in field settings.